The present invention generally relates to the electrotechnical field and relates, more precisely, to a method for controlling a battery charger, usable notably in an electric vehicle for controlling the charging of a drive power battery of such a vehicle.
In order to make durable mobility accessible to all, it is necessary to develop electric vehicles that are low cost and rechargeable over the home electrical power network. Such vehicles preferably have a drive power battery charger operating at low power, notably limited to 7 kW when it is connected to a single-phase AC power network.
Amongst the possible charger architectures may be differentiated, on the one hand, the chargers using a transformer with a galvanic isolation between the external electrical supply network and the vehicle to be charged, referred to as isolated chargers, and, on the other hand, the chargers not isolated from the external electrical power network. Isolated chargers are preferred for the simplicity of the management of the electrical safety during the charging of an electric vehicle incorporating such an isolated charger, despite the slightly higher cost and additional volume to be provided owing to the integration into the charger of a galvanic isolation transformer.
The French patent application FR3001091 describes an isolated charger for electric vehicles designed for a slow charging process at 7 kW over a single-phase external electrical power network. This isolated charger comprises an input rectifier stage connected, at its output, to a DC-DC converter stage, itself connected at its output to the drive power battery via a voltage step-up stage.
The DC-DC converter stage itself comprises:                an inverter whose input is connected to the input rectifier stage and whose output is connected to a resonant circuit,        the resonant circuit connected to the inverter,        a galvanic isolation transformer integrated into the resonant circuit which comprises in series the primary winding of the transformer, a resonance capacitor and a resonance inductor,        a rectifier whose input is connected to the secondary winding of the transformer and, at its output, to the step-up stage which is connected to the drive power battery of the vehicle.        
In order to limit the losses during the transfer of energy from the supply network to the battery, the components of the resonant circuit are chosen in such a manner that the transfer of energy within the transformer can take place at the frequency of resonance of the resonant circuit. The inverter is then controlled so as to produce an AC current at the resonance frequency. For this purpose and in order to reduce the switching losses, the transistors of the inverter are therefore switched at high frequency in such a manner that their switching is carried out at zero voltage (switching known as ZVS for “Zero Voltage Switching”) and at zero current (switching known as ZCS for “Current Voltage Switching”), at the resonance frequency.
This type of isolated charger requires a precise matching of the components of the isolated charger, and notably of the resonant circuit, in order to obtain an adequate performance and so as not to cause oscillations which would cause the destruction of the transistors by charge overlap in the junctions.